An organic electroluminescence (EL) device is generally composed of an anode, a cathode, and one or more organic thin film layers sandwiched between the anode and the cathode. When a voltage is applied between the electrodes, electrons are injected from the cathode and holes are injected from the anode into a light emitting region. The injected electrons recombine with the injected holes in the light emitting region to form excited states. When the excited states return to the ground state, the energy is released as light.
Many researches have been made on the applications of organic EL device to display, etc. because of its possibility of a wide selection of emission colors by using various emitting materials in a light emitting layer. Particularly, the research on the materials which emit three primary red, green, blue colors has been made most actively, and the intensive research has been made to improve their properties.
One of the most important issues in the organic EL device is to achieve both high emission efficiency and low driving voltage. It has been known that a highly efficient light-emitting device is obtained by a light emitting layer wherein a several percent of a dopant material is doped into a host material. The host material is required to have a high carrier mobility and a uniform film-forming property, and the dopant material is required to have a high fluorescent quantum yield and a uniform dispersibility.
Patent Document 1 discloses a compound having a carbazole skeleton as the material for such a light emitting layer. Non-patent Document 1 discloses a compound wherein a 7-membered ring is fused to a carbazole structure, however, teaches or suggests nothing about its use as the material for organic EL device.